light transmission amplitude of excitation is low enough to not cause collisions between neighboring...
TRANSCRIPT
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Light Transmission
Amplitude of excitation is low enough to not cause collisions between neighboring molecules. The beam then is transmitted consecutively across the material.
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Glass Is Opaque to UV & IR
•IR & UV:•Excitation amplitude is large → Lots of collisions!•Initial energy from light lost to thermal energy
•Visible:•Excitation amplitude is small → Collisions less likely•Absorbed light beam gets re-emitted through material
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Glass Protects you From Sunburn!
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Pierre de Fermat
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Theorem Proved!
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Fermat’s Principle of Least Time
Light will always take the path from one point to another that minimizes the
time of its journey.
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What About for Reflecting from a Mirror?
Mirror
Quantum mechanically, they all (including all the possibilities that have not been drawn) happen!
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What’s the One That’s Seen?
Mirror
A
B
Equidistant to Mirror
B’
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Law of Reflection
Mirror
A
BNormal to
Mirror
θi θr
θi = θr
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Mirror Image
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I’m Floating!!
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Transmission (Revisited)
Visible light can pass through certain materials (e.g., glass).
Question:Does the speed of light change in going
from one transparent medium into another?
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Transmission (Revisited)
It takes time for the light to be re-emitted when captured → Slows down!
Speed of light in medium Speed of light in vacuum
Index of Refraction
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Indices of Refraction for Various Materials
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How Slow Can Light Go?
In ultracold sodium (at temperatures around 1 nK = 1 x 10 -9 K):
v = 17 m/sThat’s about 38 miles/hour!
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Which One Is The Shortest Distance?
ABC
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Which One Takes The Least Time?
ABC
Running → Fast
Swimming→ Slow
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Light Behaves the Same Way!
•As light enters from a medium with a LOW index of refraction to one with a HIGH index of refraction, the ray bends TOWARDS the normal.
•As light enters from a medium with a HIGH index of refraction to one with a LOW index of refraction, the ray bends AWAY FROM the normal.